1. Field of the Invention
This invention relates to communications system generally, and more particularly to a time-division multiple-access communications protocol for use in a multi-user computer system.
2. Description of the Prior Art
A personal computer typically contains a processor, memory, storage devices, printer, etc., and is ordinarily used in a single-user environment. A personal computer may also be connected to a computer network to share common resources such as mass storage devices, printers, database, etc, with other computer systems. However, the cost of setting up and maintaining a computer network is ordinarily beyond that which a small office or a family can include within their budget. A solution is to provide an inexpensive multi-user computer system for use in a small office or home.
A multi-user computer system may accommodate the need of a networked computer system in a small office or a home. A multi-user computer system typically contains a base unit and at least one front-end unit for user interface. The base unit usually contains the typical components of a computer system, such as a processor, memory devices, and mass storage devices. It also contains input devices, such as a keyboard or a mouse, and output devices such as a monitor and a printer. The front-end units may include a display monitor, a keyboard, and a mouse. The multi-user computer system described above may substitute the network computer system for use in a family or small office, because such a multi-user system may be used by multiple users simultaneously. In such a multi-user system it is essential that the processor possess a strong processing power to accommodate the operations requested by the base unit and the front-end unit.
The personal computer industry has experienced tremendous growth in the last decade. Personal Computers are now both affordable and ubiquitous. Storage devices are more compact in size yet have a much higher storage capacity. Processors have much higher processing power than their typical usage requires and display devices are capable of displaying color video graphics instead of merely monochrome text. It is now possible to apply the multi-user concept in a personal computer system. This can be accomplished by adding to a personal computer front-end units that utilize the processor's processing power and the storage devices' storing capacity.
One of the difficulties in providing such a multi-user computer system is in transmitting the video signals from the base unit to the front-end unit. In an IBM Personal Computer compatible system, 15 signals are required to drive a color display on a color video monitor. The 15 signals include Red, Green, and Blue (RGB) colors and their respective return signals, and horizontal synchronous (H-Sync), vertical synchronous (V-Sync) and ground signals. A keyboard requires five signal lines, and a mouse requires 9 other lines. Hence, to support a front-end system that utilizes a color video display, a keyboard, and a mouse for a typical Windows environment, a minimum of 29 signal lines is required. One may use a cable to transmit all of the relevant signals from the base unit to the front-end unit. However, the RGB signals are transmitted in analog format. They need to be shielded to prevent them from interfering with other devices within its proximity. Analog signals that drive the analog monitor can only be transmitted within [its] their proximity. Hence, this limits the front-end unit's distance from the base unit.
Moreover, most of the systems utilize a cable of only a few feet in length for transmitting the video signals to the monitor. This limitation substantially restricts the location of the auxiliary unit to be within the proximity of the processor. It is desirable that auxiliary unit be located in a different room than the base unit. Hence, it is desirable that the video signals can be transmitted for a longer distance to a remote location.